U.S. Pat. No. 315,403 describes a screw closure cap of plastic material associated with a receptacle, the cap comprising a circular guarantee ring connected to the body of the capsule by breakable bridges. The neck of the receptacle carries profiled faces or "ratchet teeth", and the guarantee strip carries internal teeth co-operating with the ratchet teeth, latter being elastically inclinable in the direction of screwing in order to allow the cap to be screwed on without breaking the breakable but then preventing its being unscrewed without these bridges being broken, the ratchet teeth then being elastically straightened.